Study on Tool Life and Surface Roughness of High Speed Milling of Hardened Steel by Small Size Ball End Mill

In this paper, the flank wear and the surface roughness of a machined surface are investigated by high speed milling of hardened steel on a small size ball end mill using a high speed spindle attachment. And also an investigation is carried out on the influence of a tool life on the minimum quality lubrication (MQL) method. The main results are as follows. (1) The flank wear of the cutting edge increases in proportion to the cutting length, and the flank wear shape gradually brings the shape of the actual cutting length close. (2) It is shown that the long tool life is obtained by the conditions of the step down pick feed and the down milling with MQL method to the end point of each milling process. (3) The surface roughness increases in proportion to the cutting length. But using the same cooling method described in (2), the small surface roughness of 3 μm is obtained till 2000m of cutting length. (4) Under the cutting conditions, bidirectional milling is an effective milling method by reason of the shortest cutting time that is about 70% of other types of milling and the longer tool life that is about 90% of the maximum tool life obtained by down milling.